Temperature-responsive device



I. J. BARSY TEMPERATURE-RESPONSIVE DEVICE March 10, 1953 2 SHEETS-SHBETl Filed Dec. 22, 1948 gywe/Mcw IMRE J. BARSY March 10, 1953 l. J. BARSYTEMPERATURE-RESPONSIVE DEVICE Filed Dec. 22, 1948 THERMAL JUNCTION 2SHEETS--SHBET 2 coNsTANTAr T CONSTANTAN ""coPP'1-:'R""

CONSTANTAN b ss SOURCE OF 3mm H.F. VOLTAGE mm: J.BAR$Y 0 law. 161*Patented Mar. 10, 1953 TEMPERATURE-RESPONSIVE DEVICE Imre J. Barsy,Lancaster, Pa., assignor to Armstrong Cork Company, Lancaster, Pa., acorporation of Pennsylvania Application December 22, 1948, Serial No.66,670

3 Claims.

This invention relates to a temperature-responsive device and isconcerned particularly with a device for use in connection with highfrequency heating equipment where the high frequency currents may pose aproblem of proper temperature response and control or indication.

The invention will be useful in many fields, although the embodimentswhich will be particularly described are designed for use in themanufacture of cork compositions and like masses, dielectrically heatedwithin a mold and under compression.

In the manufacture of such products where high frequency currents areused to efiect the elevation of the temperature of the mass, it isdesirable, as specifically described nd claimed in the copendingapplication of George E. Gard, Serial No. 702,559, filed October 10,1946, and entitled "Method and Apparatus for Dielectric Heating, nowPatent 2,508,382, to provide a temperature-responsive device which maybe directly inserted into the mass of material under treatment, thedevice being electrically connected to indicating and controllingequipment efiective for maintaining a desired temperature within themass and for discontinuing the supply of the heating current uponcompletion of the baking cycle. A probe type temperature-responsivedevice suitable for use with systems such as those of the Gard inventionis disclosed in my copending application, Serial No. 750,2 5, filed May24, 1947, and entitled Temperature-Responsive Devices, now Patent2,609,406. Where probe type devices are employed, utilizingthermocouples as the thermo-sensitive elements, the hollow highfrequencycurrent conductor through which the thermocouple leads pass is split toelectrically isolate one thermoccuple and its probe tube from the other,and a condenser is disposed across the two sections for the flow ofstray high frequency currents to ground while preventing the flow ofsmall high frequency currents in the thermocouple circuits. This is arather cumbersome arrangement; and, in order to be on the safe side andavoid any possible damage to the temperature recording and controlinstruments, it is necessary to use a relatively large condenser.

The probe tube, the supporting and actuating assembly, and the portionof the split conductor connected thereto constitute an electrical systemof substantial exposed area which acts undesirably to permit the flow ofhigh frequency currents therein, leading to false temperatureindications and improper control. It is not possible to insulate thethermocouples or other thermosensitive elements at the tip of the probedisposed within the mass and thus reduce the capacitance effect of thesystem and also obtain the desired isolation of the thermocouplesbecause it is essential that the probe tube be of relatively smalldimensions in order to be readily inserted and withdrawn from the mass,and also in order to avoid the formation of an objectionable opening inthe mass upon completion of the baking cycle and removal of the probetube. The tip must also be of as small a mass as possible. in order toobtain high sensitivity of the thermosensitive elements. The use ofelectrical insulation at the tip would also reduce the heat sensitivityof the device, since the insulation would impede the rapid transfer ofheat from the mass under treatment to the thermo-sensitive elements.

It is an object of this invention to provide a temperature-responsivedevice which is essentially free of any tendency to provide a path forhigh frequency currents which would adversely aii'ect proper control ortemperature indication.

Another object of the invention is to provide a temperature-responsivedevice of small size and high sensitivity which constitutes anelectrical system of small surface area in the portion exposed to thehigh frequency field.

A further obiect of the invention is to provide a temperature-responsivedevice including a probe tube, a thermo-sensitive device electricallyconnected to the tube, and a supporting holder, with the tube and holderelectrically isolated from each other.

An additional object of the invention is to provide atemperature-responsive device which will eliminate the need for a splitconductor and condenser arrangement.

Generally, the device comprises a metallic probe tube which is adaptedto be disposed within the mass under treatment. A thermo-sensitiveelement such as a thermocouple is disposed within the tube andelectrically connected thereto. Preferably, this connection is made atthe very tip of the probe tube by soldering. A shielding holder isprovided for the tube and surrounds a portion thereof, providing a pathto ground for stray high frequency currents. Electrical insulation isdisposed between the probe tube and the holder, thus electricallyinsulating the two, one from the other. This arrangement provides aclose coupling to ground.

In another aspect of the invention, I provide an apparatus fordielectrically heating a mass of material disposed between electrodesupon which may be impressed a high frequency voltage, comprising athermal-responsive device adapted to be disposed within the mass duringthe dielectric heating, and comprising a metal probe tube, athermo-sensitive element disposed within the tube and electricallyconnected thereto, a shielding holder for the probe tube, and electricalinsulation between the tube and holder. There is provided in thiscombination electrical means controlled by the thermal-responsive deviceand electrically connected to the thermo-sensitive element by leadswhich pass through the probe tube and the holder, and means are providedfor connecting the holder to ground. This apparatus is arranged toprovide a close coupling to ground, and high frequency currents do notaffect the temperature recording or control equipment.

The invention is illustrated in theattached drawings, in which: 7 Figure1 is a sectional view illustrating a preferred form of probe device;

Figure 2 is a sectional view illustrating a modified probe device;

Figure 3 is a sectional view of a preferred tip structure for the probetube;

Figure 4 is a schematic diagram showing the interconnection of a pair oftemperature-responsive devices with suitable temperature indicating andcontrol equipment; and

Figure 5 is a diagrammatic view illustrating the disposition of a pairof temperature-responsive devices within a mass of cork compositiondisposed within a mold for high frequency bakins.

Referring first to Figure 1, the device includes aprobe tube 2 having atip 3. The tube is preferably formed of Inconel which is an alloy of 80%nickel, 13% chromium, and'the balance iron. It is resistant to corrosionand to heat and retains its strength after repeated heating and cooling.It. has good resistance to bending. Disposed within the tip 3 is athermo-sensitive element 3 in the nature of a thermal junction includingtwo'negative leads and one positive lead. The positive lead 5 may beformed of copper; the negative leads 6 and l of constantan. The Wiresare twisted together and inserted into the tip. Preferably, the twistedwires are coated With silyer solder and are soldered into the tip so asto provide good heat conductivity from the junction to the body of thetip and to properly anchor the thermal junction to the tip. Theconstantan wires may be B & S gauge No. 28 and are preferably insulatedbeyond the junction with glass fiber insulation impregnated with asilicone resin. Thecopp'er element may likewise be of B & S gauge No. 28and similarly insulated. The diameter of the twisted wires constitutingthe junction 4 should preferably be just slightly less than the innerdiameter of the opening in the tip which receives them so that there isbut a thin film of silver solder required for making the electrical,thermal, and mechanical connection with the tip, thus assisting inattaining the desired high degree of sensitivity.

The probe tube 2 is received within a holder 8 which includes'asubstantiallycylindrical portion 9 which is adapted'to be mounted in asuitable bearing, not shown, so that the probe may be mechanicallyinserted into the mass under treatment and withdrawn therefrom. Theholder 8 also includes a connector portion l threaded at [I to receive astandard electrical connector, such there is inserted therein a hollowcylindrical piece of electrical insulation [3, which insulation ispreferably heat-resistant, a good dielectric, and has superiormechanical characteristics. Material known as Mycalex 400 consisting ofa glass bonded mica insulation is satisfactory. The opposite end of theholder is bored as indicated at It and receives a hollow cylindricalpiece of insulation l5, which may be of the same composition as theinsulation l3. Between the bores l2 and HA is a central bore I6 whichreceives a hollow cylindrical piece of insulation I1. This piece may beformed of Mycalex but preferably it is formed of Teflon which ispolytetrafluoroethylene.

The insulation element I5 is provided with a bore it having a conicalbottom IS, the taper of which corresponds to a taper provided on the end29 of the probe tube 2. A compression plug 2| of insulation which may bethe same as the insulation element i5 is provided, having an outerdiameter corresponding to the diameter of the bore 18 and having atapered surface 22 corresponding to the taper of the end 20 of the probetube 2. The portion I!) of the holder 8 is provided with a screw threadprojection 23 which receives a hollow head, fiat based screw 2d. The

screw 24 and the compression plug 2| are centrally bored to provide apassage through which the leads from the thermal-responsive elements maypass from the interior of the probe tube'2. The openings within theinsulation elements I5 and ii are of such size that a light friction fitis provided between these elements and the probe tube 2, but theinsulation element it is bored so as to provide a tight friction fitwith the probe tube 2 in order to properly support the tube to' preventlateral or radial displacement during insertion of the probe into themass under treatment.

In the assembly of the device, the insulation elements are fitted intothe holder 8, with the exception, of course, of the compression plug 2|The probe tube 2 is then inserted into the central bores in theinsulation pieces and pressed to a position with its flanged end 20disposed in the bore Id of the insulation piece [5. The compression plug2| is then inserted and the hollow head screw 24 is threaded intoposition, forcing the compression plug 21 into the bore l8, and seatingthe probe tube in proper position, as indicated in Figure l.

A single piece tip 3 is shown in Figure 1. This tip may be formed of awear-resistant, heat-conductive material such as an alloy of copper andberyllium. Where greater heat sensitivity is necessary or desirable, afabricated tip such as shown in Figure 3 may be employed. In thisembodiment, the ogival portion 25 of the tip is made of substantiallypure silver, which has about the highest thermal conductivity of knownmaterials, a low specific heat, and is reasonably resistant to wear. Theportion 25 is connected to a shank portion 25 which may be formed of analloy of copper and beryllium. The two portions are elec trically andthermally connected by silver solder used to join the thermocouplejunction to th tip.

For example, a silver solder having a melting point of about 1300 F. maybe employed at the joint 21, and a silver solder having a melting pointof 1160 F. tov 1175 F. may be employed for connecting the thermaljunction to the tip. It

will be noted that the ogival portion 25 is provided with a bore 28which extends to a point close to the outer periphery of the tip. It isin this bore 28 that the thermocouple junction is secured. There is alarger diameter bore 29 which extends throughout the shank portion 26and into the tip portion 25 which receives the insulated portions of thewires constituting the thermal junction. It should be borne in mind thatinFigures l, 2, and 3 the parts are shown to greatly enlarged scale. Forexample, the over-all length of the device may be about 14 inches withthe total length of the tip shown in Figure 3 being but .334! and adiameter of .140 and the bore 28 having adiameter of .036".

A modification of the device is shown in Figure 2. It includesa probetube 30 which may be made of material similar to the probe tube 2. Theprobe tube has a tip 3| which may be formed in the same manner as thetip 3 of Figure 1, or the tip shown in Figure 3 may be substituted. Theprobe tube 30 is received within a holder 32, having an outerconfiguration generally the same as the holder of the device ofFigure 1. The holder 32 is bored at 33 to provide an opening for thereception of a piece of electrical insulation 34 which may be the sameas the insulation membersl3 and i of Figure 1. This hollow cylindricalpiece 34 is provided with a tapered projection 35 adapted to receive thecorrespondingly tapered end 35 of the probe tube 30. A compression plug31 of insulation is provided. This insulation may be the same as thepiece 34. The piece 31 is provided with a centralbore 38 which receivesthe probe tube 30 and is provided with a tapering recess 39corresponding in taper to the portion 36 of the probe tube. A cover cap55 is threaded onto the end of the holder 32 and is provided with acentral opening 4| which is of larger diameter than the outer diameterof the tube 35. A central bore 42 is provided within a web 43 in theholder 32 for the passage or" the leads from the thermal junction 44. Ascrew thread projection 45 is provided on the opposite end of the holder32 to receive an Amphenol or similar connector. In the assembly of thedevice, the piece 34 is disposed within the bore 33 and the tube 30 isforced through the piece 31. A tight friction fit is provided betweenthe tube 30 and the piece 31, in order to properly support the tubeagainst deflection. The tube and insulation piece are then inserted inthe bore 33 and the clamping cover cap 45 is screwed down into position,forcing the elements into the position shown in Figure 2 and firmlyclamping the tube against displacement.

It will be observed that in both devices the "therrno-sensitive elementis electrically connected to the probe tube and the probe tube iselectrically insulated from its supporting holder. The capacitance ofthe device of Figure 2 is less than that of Figure 1, but in neither isit of such magnitude that it will deleteriously affect the indicatingand control equipment or lead to any substantial errors in temperaturereading or effective control.

Figure 4 diagrammatically illustrates a typical installation wheretemperature-responsive devices of the present invention are employed.There is illustrated a mass 43, such as a mass of cork composition beingdielectrically heated in a mold between electrodes upon which isimpressed a high frequency current. There are two i pro es. shown in Eiereao disposed adjacent one edge of the mass, and the other disposedabout centrally of the mass. In the proposed arrangement, it is desiredto control the supply of high frequency current to the electrodes inaccordance with the temperature attained by the mass, and since theremay be some variation between the temperature adjacent the electrodesand at the center of the mass, the arrangement includes two temperatureresponsive devices. The temperature-responsive device disposed near oneedgeof the mass is numbered 41 and a second element disposed at thecenter of the mass is numbered 48. The device 41 includes onethermocouple 45 with a negative lead 50 and a positive lead 5|, and theelement 48 includes a thermal junction 52 with two negative leads'53 and54 and one positivelead 55. The probe tubes 56 and 51 have beenindicated by dotted lines in Figure 4, and it will be observed that theyare disposed within holders 58 and 59, 11381360? tively, and that theholders are insulated from the tubes by insulation 60 and 6|. Theholders 58 and 59 are connected to ground by leads .62.

The leads 54 and 55 are connected to a temperature recorder 63, and thisrecorder includes an arrangement for supplying energy to a control 84which is effective for cutting off the supply of high frequency power tothe electrodes between which the mass under treatment is disposed. Thus,when the mass attains the desired end temperature at its center thethermocouple 52 will have supplied sufiicient direct current to thedevice 63 to indicate proper curing temperature and simultaneouslyactuate the control 64. The lead 53 of the thermocouple 52 is connectedto a potentiometer 65, the other side of the potentiometer is connectedto the thermocouple 49 by the lead 5!], while thermocouples 49 and 52are interconnected electrically by joining the positive leads 5| and 55.In this arrangement, the potentiometer 65 is actuated by the temperaturedifference existing between thermal junctions 49 and 52, and in turn,the potentiometer is effective in actuating, through a discriminatingcontroller 66, a control 6'! for decreasing the high frequency power anda similar control 68 for increasing the high frequency power inaccordance with the aforementioned differences in temperatures betweenthose at the thermocouple 49 and the thermocouple 52. Thus the heatingof the mass may be effectively controlled in accordance with temperaturedifferences within the mass. This is particularly desirable where theelectrodes are heated, for it makes possible the proper application ofhigh frequency current to the mass to obtain substantially uniformheating as is more fully set forth in the Gard application referred toabove.

The present invention is not limited to use with the specific indicatingand controlling arrangement illustrated and described but is applicableto any system including electrical means actuated by thethermal-responsive device.

Figure 5 is a diagrammatic view illustrating the disposition of thethermal-responsive elements of Figure 4 in a mold, such as disclosed inthe copending application of George W. Scott, Jr., Serial No. 678,215,filed June 21, 1946, and entitled Mold for Confining Material DuringDielectric Heating, now Patent 2,526,698. Corresponding numbers havebeen applied to the thermalresponsive elements, numbers 41 and 48, aswell as to the ground connection 62. The mold has been indicated at 69and the mass at 10. The

mass is disposed between an upper electrode "ll between said electrodes,.(4)

and: a lower-i electrode; 12;. the electrodes" being held in; positionby through. pins. '13: disposed above and below theupper; andlower-electrodes .and ..rholding* the mass. 10 under-the desireddegree": of compression. The electrodes. are connected to a source 'iOfhigh frequency voltage which-has been designated onthe drawing. Thecontrol systemirom the thermal-responsive elementss ll. and 4'8 maybe-th'ersame as that shown imFigure'i 41..

The. present invention is. not: limited to a system' whereinthermocouples are'employed. .Fine w-irei resistance elements may besubstituted .for oneor: m'orelof Fth'e thermal. junctions, andthermistors and other-similar thermally sensitive devices. may besubstituted.

-:While lahavesillustrated and described certain preferred.em'b'odimentsnof my invention, it. will tberunderstood the same isnotlimited thereto but maybe otherwise-embodied and practicedxwithintrodestoa source of highfrequency alternating electric currentitoestablishahigh frequency field a temperatureresponsivedevicedisposedadjacentto one of said -electrodes within saidiield duringdielectric heating-10f; a mass positioned vbetweensaid electrodes, *(5')'a second ztemperature-responsive device positioned within said fieldand at a .difierent high irequencyipotentialithan said othertemperature- Iesponsive' device, each of said temperature responsivedevices; comprising: (a). a. metallic "probe tube having a. projectingportion, (22) a thermocouple electricallyconnected to said :probe :tubelat the end of the projecting portion thereof,

(0) thermocouple .leads extending through said probe-tube-(d)? a layerof electrical insulation surrounding the remaining portion of said probetube, and '(c) a metallic shielding holder surrounding said insulation,(6). an electrical connectionibetween elements of saidthermocouples.offioneizpolarity,.(7) an electrical control device responsive. todirect current of small magnitude delivered thereto from elements ofsaid thermocouples of the other polarity in response to telniperaturedifferentials existing between: said thermocouples; and 1(8) acapacitative couplin to ground to render each unit'of'a thermocouple:andit's 'leadsdisposed within saidfield at'different high frequencypotentials essentially free of any tendency. to provide'a path for highfrequency current tov said electrical control which would afiect-saidicontrol, said coupling to ground for each unit comprising: (a) saidmetallic shielding holder, (b). said metallic probe tube to which saidthermocouple is electrically connected, (0) said electrical insulationlayer disposed between said -metallicrprobe tube tand saici metallicholder, and

(d) a ground lead electric'allyrconnected to each :said metallicshielding holder.

7 '2; In an apparatus for dielectrically-heating' a mass Ofmaterial: (1)afirst electrode, (2) asecmidi-electrode; ('3) means connecting saidelec- "trodesto asource of'high frequency alternating electric currentto establish ahigh frequency field between. :said electrodes, (4)

a temperatureresponsive: device disposed adjacent to one of said 8: saidelectrodes andzata different high frequency potential than said othertemperature-responsive device, each of' saidtemperature-responsivedevices comprising: (a) a metallicprobe tubehaving an exposed portion for insertion into said mass, (19-) athermocouple electrically connected to said probe tube at theend oftheexposed portion thereof, (0) thermocouple leads extending throughsaid probe tube, (d) a layer of electrical insulation surrounding :theunexposed portionof said tube,- and (e) ametallidshieldingholdersurrounding. said insulation, '(6) an electrical connectionbetween-elements of said thermocouplesof onepolarity,v (7) an electricalcontrol device responsive to direct current of small-magnitude deliveredthereto from elements of said thermocouples of the'other polarity inresponse to temperaturedifferentials existing between saidthermocouples, and (8) acapacitative coupling to ground to render eachunitof a thermocouple and its leads disposed within said field atdifferent highzfrequency potentials essentially. free of any tendency toprovide. a path for high frequency current tosaid electrical controlwhich would aifect said control, said coupling to ground for each unitcomprising: (a) said metallic shielding holder, (12) said vmetallicprobetube. to which said thermocouple is electrically'connected, (c) saidelectrica1 insulation layer. disposed between said metallic probeitubeand said .metallic holder, and (d) aground lead electrically connectedto each said metallic shielding holder.

.3. In an apparatus for dielectrically'heating'a massof material: '(1')a first electrode, (2) asecondelectrode. (3) means connecting saidelectrodes to a source of high frequency alternating electric current toestablish .a high frequency 'field between said electrodes, (4) atemperatureresponsive device disposed adjacent to one of saidelectrodeswithin said field during dielectric heating of a mass positioned betweensaid electrodes, (5) a second temperature-responsive device positionedwithin said field andat-a-difierent high frequency potential than saidother temperature-responsive device, each of said temperature-responsivedevices comprising: (a) a metallic probe. tube having a projectingportion,z (b) a thermocoupleelectrically connected to said probe tube atthe end of the projecting portionthereof, (c) thermocouple leadsextending, through said probe tube, (cl) a layer. of electricalinsulation surroundingjthe remaining portionof said probe tube; and (e)a metallic shieldingholderasurirounding. said insulation, the second ofsaid thermocouples having a plurality-oi elements of one polarity; and asingle. thermal junction, (6) an electrical connection between saidelements of said. thermocouples of one polarity, (7) an electricalcontrol device responsive to directcurrent of: small magnitude deliveredthereto from one. of saidplurality of elements of one polarity ofsaidsecond thermocouple and an element of the same polarity of said otherthermocouple iniresponse totemperature diflerentialsexisting betweensaid 9 affect said control, said coupling to ground for each unitcomprising: (a) said metallic shieldingholder; (b) said metallic probetube to which said. thermocouple is electrically connected, (c) saidelectrical insulation layer disposed between said metallic probe tubeand said metallic holder, and (d) a ground lead electrically connectedto each said metallic shielding holder.

IMRE J. BARSY.

REFERENCES CITED The following references are of record in the file ofthis patent:

Number UNITED STATES PATENTS Name Date Sykes Sept. 29, 1931 States Aug.20, 1935 Mitchell July '7, 1936 Hawksley Dec. 22, 1936 Thomas Feb. 23,1943 Richmond Mar. 7, 1944 Lamberger et a1. Oct. 24, 1944 Kretsch et a1Apr. 20, 1949 Gard May 23, 1950 Drugmand May 23, 1950

